package 寒假作业.LeetCode;

public class Num21 {
      public class ListNode {
      int val;
      ListNode next;
      ListNode() {}
      ListNode(int val) { this.val = val; }
      ListNode(int val, ListNode next) { this.val = val; this.next = next; }
  }
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        if (l1 == null && l2 == null){
            return l1;
        }
        if(l1 == null){
            return l2;
        }
        if (l2 == null){
            return l1;
        }
        ListNode newHead = new ListNode();
        if(l1.val <= l2.val){
            newHead = l1;
            newHead.next = mergeTwoLists(l1.next,l2);
        }else {
            newHead = l2;
            newHead.next = mergeTwoLists(l1,l2.next);
        }
        return newHead;
    }

}
